It was all very exciting. A crowd of journalists in Cannes was invited to a special presentation of "footage" of Quentin Tarantino's new film Django Unchained on Monday night at the Majestic Hotel on the Croisette, outside which there is a poster for the movie so massive it can be seen from space. We had been told to arrive in good time because the screening would begin precisely at 7.30pm.

Critics, bloggers and people in suits gathered in a large antechamber, sipping wine and feeling skittish yet solemn, like cardinals who had been invited to inspect a newly discovered splinter of St Francis's femur.

An executive from the Weinstein Company mingled, reminding us of the ground rules. Reviewing the film on the basis of what we see tonight? Not on. Tweeting photos of the poster that was here in the room? So not cool. Getting your smartphone out, recording the Django footage in its entirety and uploading it to your pay-per-view website? Harvey Weinstein will personally scourge you with the silver-tipped flail he keeps for this purpose.

In fact, there were three films of which we were being offered a teasing glimpse: Paul Thomas Anderson's The Master (possibly a fictionalised version of L Ron Hubbard), David O Russell's The Silver Linings Playbook – and Tarantino's Django.

Seven-thirty sharp became seven-thirty blunt, which morphed into 7.39 on the dot, and then Harvey Weinstein himself materialised in the middle of the room, strolling through towards the screening room with the fat man's rolling gait. He cordially called out to someone, pointing, and raising his voice only slightly: "Hey, Jeff. That was kinda fun last night, wasn't it?"

Jeff breathed back sensually: "Yeah."

What was? What was kinda fun? The rest of us pondered, awestruck. What possible epicurean pleasure could Harvey have shared last night with Jeff?

The event began. Inevitably, these batches of "footage" were in fact extended and glorified trailers. The Anderson and the Russell came and went and then Django was up.

Django Unchained is about something on which Hollywood is traditionally very reticent: slavery. To the music of Johnny Cash and James Brown, a weird drama of violent revenge in the Old South unfolds. Christoph Waltz is a bizarre travelling dentist, whose profession is, in fact, a cover for his activities as bounty hunter, gunfighter and assassin.

With maximum and freaky violence, he frees a slave called Django, played by Jamie Foxx, and they track down some brothers with whom he has business.

Django wears an electric blue suit and a stylishly raked hat, and they encounter a very haughty slave owner, played by Leonardo DiCaprio. We don't get to see what Samuel L Jackson actually does in the movie, other than checking him in the credits.

The footage looks good – of course it would – but it's impossible to tell what the movie is going to be like. It could be brilliant, like Kill Bill, or underwhelming like Inglourious Basterds. Well, the chains come off at Christmas and we'll see then.